1. Field of the Invention
The present invention relates generally to an off-carrier fluid supply system and, more particularly, to a fluid height backpressure system for supplying fluid to a printhead and a backpressure device used therein.
2. Description of the Related Art
Thermal inkjet printers apply ink to a print medium by ejecting small droplets of ink from an array of nozzles located in a printhead of a printhead cartridge. An array of thin-film resistors on an integrated circuit on the printhead selectively generates heat as current is passed through the resistors. The heat causes ink contained within an ink reservoir adjacent to the resistors to boil and be ejected from the array of nozzles associated with the resistor array. A printer controller determines which resistors will be “fired” and the proper firing sequence so that the desired pattern of dots is printed on the medium to form an image.
Replacement printhead cartridges include integrated ink reservoirs. Due to weight limitations, these reservoirs usually contain much less ink than the printhead is capable of ejecting over its intrinsic lifetime. The useful lifetime of a printhead cartridge can be extended significantly if the integrated ink reservoir can be refilled. Several methods now exist for supplying additional ink to the printhead after the initial supply in the integrated reservoir has been depleted. Most of these methods involve continuous or intermittent siphoning or pumping of ink from a remote ink source to the print cartridge. The remote ink source is typically housed in a replacement ink tank which is “off-carrier,” meaning it is not mounted on the carriage which moves the printhead cartridge across the print medium. In an off-carrier ink supply system, the ink usually travels from the remote ink tank to the printhead cartridge through a flexible conduit. It is desirable to maintain a backpressure in the off earner ink supply system to prevent drooling of ink from the printhead nozzles.
Most off-carrier ink supply systems use one of two general methods to accomplish the required backpressure. Some use an onboard pressure regulation system. These have been configured to use either an intermittent refill system (periodic ink re-supply) or a generally pressurized continuous ink supply that re-supplies ink to the printhead when a valve is opened. The other type of system is passive and uses the off-carrier fluid height to supply the proper backpressure (negative pressure) to the printhead. The second type of system may use a vented intermediate tank.
Pressure regulation systems are generally independent of the supply height and have greater flexibility in supply location. The second type of system is simpler, but must have the ink supply or an intermediate ink tank at a particular height below the printhead. The limited supply location is a drawback with this type of system and becomes more of a problem as a user prefers smaller and smaller machines. Although backpressure can be added by use of spring loaded diaphragms, this tends to add complexity and cost.
Consequently there is a need for an innovation in a fluid height backpressure system for supplying fluid to a printhead that addresses the location issue without adding complexity to the supply.